University of Minnesota
School of Physics & Astronomy


Observations of Large Amplitude, Narrowband Whistlers at Stream Interaction Regions


Breneman, A., C. Cattell, S. Schreiner, K. Kersten, L.B. Wilson III, P. Kellogg, K. Goetz, and L. K. Jian (2010), J. Geophys. Res., doi:10.1029/2009JA014920, in press.

We present the first solar wind observations of large amplitude,
narrowband waveforms in the frequency range 10-100 Hz, consistent with the whistler mode. These whistlers are only observable in high time resolution electric field waveform data provided by the Time Domain Sampler (TDS) instrumenton STEREO. Amplitudes range from a few to >40 mV/m peak-to-peak,one to three orders of magnitude larger than any previous observations of whistlermode waves in the solar wind. The whistlers are obliquely propagating with a large electrostatic component and are right-hand elliptically polarized in the spacecraft,frame. The whistlers occur in groups that are strongly correlated with stream interaction regions (SIRs). The groups persist from a few seconds to minutes and are observed at 88% of SIRs and 17% of shocks from available data. A more detailed look shows that the whistler groups are observed near sudden disturbances of the solar wind magnetic field and plasma. We suggest that, due to the oblique and narrowband nature of these waves, an electron or ion beam instability may be responsible for their creation. Test particle simulations show that the waves can interact strongly with halo (>60 eV) electrons. Test electrons were scattered by tens of degrees and energized/de-energized by up to 50% in a few tens of msec. Thus these whistlers may play an important role in the dynamics of solar wind electrons within SIRs and near some shocks.

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